Patent GB-769552-A (GB)
Title: Improvements in and relating to apparatus responsive to variations in the mass content of an elongated body
Inventor: FEARNSIDE KENNETH
IPC: A24C5/34
Filed: 1952-01-09
Abstract: 769,552. Control apparatus utilizing radioactive sources. INDUSTRIAL MACHINERY CO., Ltd. April 9, 1953 [Jan. 9, 1952], No. 706/52. Class 40 (3). In, for example, a cigarette-making machine, involving apparatus sensitive to variations in the mass of an elongated body, a number of radio active sources direct radiation through the body in different directions normal to its axis. The machine described controls the rate at which tobacco is supplied and rejects those that are underweight or contain voids. Sensitive arrangement.-The assembly comprises five steel tubes 11, Fig. 1, filled with radio-active material, e.g. strontium 90 and radium D plus E, evenly spaced radially in small recesses in a copper sleeve 10 with five detectors (phosphor crystals) 12, e.g. as described in Specification 732,353, symmetrically arranged between them, but further from the axis, in slits 16, extending to the outside of the sleeve and closed to light at their inner ends by metal foils, the arrangement being such that only the three detectors opposite each source can see it. Scintillations from all the detectors are internally reflected by the walls of an annular methyl methacrylate case 18 surrounding the sleeve on to the cathode of a photo-multiplier mounted on a flattened part 19 of the annulus, the remainder of which is shrouded by 20 to exclude extraneous light. Operation of discriminator and integrator circuits (Fig. 4).-Pulses from the photomultiplier are fed through a discriminator described in Specification 732 353) and through clamp diodes V3, V4 to monostable multivibrator V1, V2. The output pulses-from the multivibrator are shaped by cathode-coupled bi-stable multivibrator V6, V7 and then fed to three diode pump circuits V8 and V9, V10 and V11, V12 and V13 which charge condenser C7 through circuits with different time constants, the end diodes being supplied with larger amplitude pulses (developed across R11 and R12) than the middle one to reduce errors. The equilibrium voltage across C7 is proportional to the logarithm of the mean pulse rate. This integrating circuit operates over periods corresponding to passage of one cigarette, its operation being controlled by square pulses of predetermined duration fed to grid of valve V17 from a phantastron V15 responsive to timing pulses from C.V17 is thus cut off, allowing C7 to charge via R17, V19 until the pulse ends when C7 is discharged through R17 and the cathode circuit of V17. The integrated voltage across R17 is amplified in V21 and fed to cathode follower V22, the output of which operates a reject mechanism, while the output of V21 is also fed to a linear integrator, operating over a longer period, comprising a diode pump circuit V23, V24, R40, C15 with a feed-back amplifier V25, V26 to produce a final output at D, proportional to average tobacco density which controls the feed. An essentially similar linear integrator fed direct from the discriminator rapidly responds to high counting rates caused by voids in the cigarettes to operate a reject mechanism.